diff --git a/sys/netipsec/keydb.h b/sys/netipsec/keydb.h
index 19e9aebdf286..363b8f99d638 100644
--- a/sys/netipsec/keydb.h
+++ b/sys/netipsec/keydb.h
@@ -35,6 +35,7 @@
 
 #ifdef _KERNEL
 
+#include <sys/lock.h>
 #include <sys/mutex.h>
 
 #include <netipsec/key_var.h>